The present invention relates generally to pattern measuring apparatus which perform pattern measurement based on pattern concavity/convexity determination or the like, and more particularly to a pattern measuring apparatus that performs pattern identification of line segments and gap spaces formed on a semiconductor wafer.
A scanning electron microscope (SEM) is one form of charged particle beam apparatus, which enables observation of fine objects. The SEM has a variety of applications, including measurement and inspection of circuit patterns that make up highly integrated semiconductor devices. Incidentally, with recent advances in miniaturization of semiconductor devices, circuit patterns increase in integration density. In particular, this has often led to appearance of ultrafine circuit patterns, known as line-and-space patterns having successive line patterns, wherein lines and gap spaces are hardly distinguishable from each other in interval or pitch. Additionally, with advances in semiconductor microfabrication technology, observation images of a line and space are becoming more similar in look to each other.
An increase in visual similarity of line and space results in the risk that one of them is mistaken for the other. More specifically, even when an image was acquired in order to measure the width of a line, it can happen in practice that the width of a space is measured by mistake. Japanese Patent Literature JP-A-2004-251674 (its corresponding United States Patent Application Publication is US 2004-A-0222375) discloses therein a technique for distinguishing between line and space portions on the basis of expansion of hem parts of a plurality of peaks contained in a differential waveform of a profile, which has been obtained by applying projection processing to an image acquired. However, sensed images tend to decrease in contrast due to further miniaturization in recent years; so, it is difficult in some cases to extract the difference in brightness of hem parts of profile peaks. Once peaks overlap each other, discrimination can be failed.
JP-A-2006-332069 (its corresponding United States patent is U.S. Pat. No. 6,872,943) discloses a technique for performing concavity/convexity determination with high accuracy by irradiating a tilted beam and emphasizing a difference between peaks of two, right and left edges of a line.